Striking advances have been made in understanding the early course of symptoms and the development of early intervention for children with autism spectrum disorder (ASD). Nonetheless, treatment response is highly variable and difficult to predict. In order to understand the individual trajectories of children with ASD (IACC, 2013), the course of associated impairments must be better understood. The goal of this BRAINS R01 project will be to launch an interdisciplinary longitudinal research program aimed at providing a detailed characterization of the NIMH RDoC domains of cognitive control and working memory as they inform the early the course of ASD. This approach provides an innovative perspective to charting the early trajectory of ASD in order to determine when, where, and how to intervene (NIMH Strategic Objective 2). Executive control is generally impaired in individuals with ASD and encompasses aspects of cognitive control and working memory (Guerts et al., 2014; Kenworthy et al., 2008). Using an accelerated longitudinal design to follow the behavioral and neural trajectories of 120 2-year-olds and 120 4-year-olds (with ASD and age- as well as IQ-matched comparison children) for three years, this project will address three critical goals: (1) to precisely determine the point at which a unique and stable profile of executive impairments first emerges; (2) to map the neural and neuropsychological profile of executive control development by examining distinct, but interrelated, subdomains of executive control in order to better understand individual differences over time; and, (3) to examine the relation between executive control and social function early in the course of ASD to determine whether executive control is critical to optimizing social outcomes. This information potentially stands to change the way early intervention is delivered for young children with ASD by providing essential information about potential biological and behavioral treatment targets and intervention outcomes for toddlers and preschoolers with ASD. It also uses electroencephaolography to provide a groundbreaking glimpse into the early, longitudinal brain development of children with ASD in the first years following diagnosis. Our interdisciplinary expertise with very young children at the Laboratories of Cognitive Neuroscience uniquely positions us to achieve these goals by building on the PI's current K99/R00 funded study that examines individual differences in executive control and treatment response to targeted executive control training among school aged children with ASD. In addition, this BRAINS project will employ an external advisory committee with expertise in the measurement of the emergence of executive function in typical development and early- targeted treatment development for children with ASD in order to (1) optimize an innovative measurement battery to characterize executive control?from diagnosis of ASD to the beginning of school, and (2) to prepare for a subsequent intervention study.